Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for better performance at lower cost. To meet these demands, the mechano-electrical assembly in a DASD device, specifically the Hard Disk Drive (HDD) has evolved to meet these demands.
In order for an HDD to hold more data, advances in the disk media in which the data is written as well as the magnetic transducer for writing and reading the data have undergone major advances in the past few years.
The magnetic transducer used in the first hard disk drives was based on an inductive principle for both writing and reading data to and from the disk media. For writing data into the disk media, electric current is passed through an electrically conductive coil, which is wrapped around a ferromagnetic core. The electric current passing through the write coil induces a magnetic field in the core, which magnetizes a pattern of localized spots in the disk media as the disk media passes close to the magnetic transducer. The pattern of magnetized spots in the media forms data that can be read and manipulated by the HDD. To read this data, the disk passes the magnetized spots of written data close to the same magnetic core used for writing the data. The magnetized spots passing close to the ferromagnetic core induce a magnetic field in the core. The magnetic field induced in the ferromagnetic core induces an electric current in a read coil similar to the write coil. The HDD interprets the induced electric current from the read coil as data.
Magnetoresistance (MR) transducers replaced inductive read heads. An MR transducer reads written data in disk media, still in the form of magnetized spots, by sensing the change in electrical resistance of a magneto-resistive element in the MR transducer. An electric current is passed through an MR transducer. The current typically traverses the MR transducer perpendicularly to the direction of disk rotation and in the plane of the MR films.
Advances in the magneto-resistive element materials have made the MR transducer more sensitive and is now referred to as a giant magnetoresistance (GMR) transducer. As with the MR transducer, the current typically traverses the GMR transducer perpendicularly to the direction of disk rotation and in the plane of the GMR films, and the data is written in the disk media with an inductive write transducer.
Further advances in magneto-resistive reading have given rise to tunneling magnetoresistance (TMR) magnetic transducers. The current traversing the TMR magnetic transducer is typically parallel to the direction of disk rotation, and perpendicular to the TMR films. A thin insulator barrier is placed between two ferromagnetic conductors. Electrons tunnel through the thin insulator barrier. The resistance of the electrons tunneling through the thin insulator barrier will change as the magnetic domain structure within the two ferromagnetic conductors react to the presence of a magnetized spot in the disk media. In this manner, data can be read that has been magnetically written in the disk media.
Continuing advances are being made in the TMR magnetic transducer design and fabrication methods as more demands are made on the performance of HDDs using TMR magnetic transducers.